1. Field of the Invention
The present invention relates to a digital phase-shifting circuit for use in a thyristor converter.
2. Description of the Prior Art
The conventional digital phase-shifting circuit of this type can be represented by the one that is shown in FIG. 1.
That is, FIG. 1 shows the conventional thyristor converter and the digital phase-shifting circuit. The thyristor converter 7 consists of thyristors 1 to 6 that are connected to three phases U, V, W of an AC power supply and to DC voltage terminals P, N. A phase-shifting circuit 19 is corresponded to thyristors 1 and 4 among the above-mentioned thyristors. The phase-shifting circuit 19 includes a binary counter 10 which counts input clock signals 8 and which produces binary outputs 18. Here, the period of operation cycle of the binary counter 10 has been brought into agreement with the period of one phase of the three-phase AC power supply by a PLL (phase-locked loop) that is not shown.
A digital comparator 12 compares a striking phase reference (value of binary notation) of the thyristor with a binary output 11 consisting of bits which do not include the most significant bit among binary outputs of the binary counter 10, and produces an output 13 of the logical level "1" when values of bits 11 exceed the striking phase reference 40. A pulse circuit 14 connected to the digital comparator 12 generates a pulse responsive to the output of the digital comparator 12, and distributes the pulse to either an output terminal 16 or an output terminal 17 alternatingly responsive to a signal 15 consisting of the most significant bit among the binary outputs 18. The outputs 16 and 17 of the pulse circuit 14 are amplified to form striking signals TU, TX for the thyristors 1 and 4.
A phase-shifting circuit 29 also works to supply striking signals TZ, TW to the thyristors 2 and 5, and functions quite in the same manner as the phase-shifting circuit 19. The phase-shifting circuit 29, however, has a reset circuit 41 for resetting a binary counter 20, and produces a reset pulse at a moment when the binary output 18 of the counter 10 assumes an electric angle of 60.degree.. The binary counter 20 is reset by the thus produced pulse.
A phase-shifting circuit 39 supplies striking signals TV, TY to the thyristors 3 and 6, and operates in the same manner as the above-mentioned phase-shifting circuit 19. A reset circuit 42, however, produces a pulse at a moment when the binary output 18 of the counter 10 assumes an electric angle of 120.degree. to reset a binary counter 30.
Operation of the thus constructed conventional device will be described below.
Counter outputs 111 of FIG. 2 (a) represent, in an analog manner, binary outputs 11 (outputs excluding the most significant bit 15 among outputs 18 of all bits of the counter 10) of the binary counter 10 in the phase-shifting circuit 19. The counter output 111 repeats the counting-up after every electric angle of 180.degree.. FIG. 2 (b) represents the output 15 consisting of the most significant bit of the binary counter 10, which is in synchronism with the period of the AC power supply.
Here, if the striking phase reference 40 is denoted by an analog quantity as shown in FIG. 2 (a), the counter output 111 crosses the phase reference 140 at phase moments of .alpha..sub.1 and .alpha..sub.4 in one cycle (i.e., in one cycle of the most significant bit 15) of the period of the power supply. At these moments, the digital comparator 12 produces output signals 13 to the pulse circuit 14 so that it will produce two pulses. These two pulses are distributed to the output terminal 16 and output terminal 17 by the signal 15 consisting of the most significant bit [FIG. 2 (b)], whereby output pulses TU, TX are prepared as shown in FIGS. 2 (c) and 2 (f), and are supplied as striking signals to the thyristors 1 and 4. The phase-shifting circuit 19 corresponding to the thyristors 1 and 4 operates as mentioned above. Phase-shifting circuits 29 and 39 corresponding to other thyristors 2, 5 and 3, 6, also, operate in the same manner as the above phase-shifting circuit 19. However, the binary counter 20 is reset by the reset circuit 41 at the moment when the output of the binary counter 10 assumes the electric angle of 60.degree.. The binary counter 30 is also reset when the output of the binary counter 10 assumes the electric angle of 120.degree.. Accordingly, outputs 21 and 31 of the counters 20, 30 assume patterns whose phases are deviated by 60.degree. and 120.degree. relative to the counter output 111 of the binary counter 10, as indicated by counter outputs 121, 131 in FIG. 2 (a). Final outputs 26, 27, 36, 37 become as indicated by (d), (g), (e) and (h) in FIG. 2; i.e., striking signals are produced for the thyristors 2, 5, 3 and 6.
According to the conventional art, therefore, the digital phase-shifting circuit device needs one complete circuit for each phase, i.e., needs three complete circuits. That is, six circuits are required when the phase-shifting circuit device is to be adapted to a six-phase power supply.
In the conventional device, furthermore, if the number of bits of binary counters is increased to increase the resolution for the phases, increased number of parts must be used for the counters and comparators of each circuit, resulting in the complicated setup and increased manufacturing cost.
In order to preclude the above-mentioned defects, the object of the present invention is to provide a digital phase-shifting circuit in which the number of counts of the counter is selected to be 6.times.2.sup.N (N is a given number) within a period of 360.degree., and counters and a comparator are commonly utilized in the phase-shifting circuit, in an attempt to reduce the number of parts.